We report on our attempt to understand the outbursting profile of Galactic Black Hole sources, keeping in mind the evolution of temporal and spectral features during the outburst. We present results of evolution of quasi-periodic oscillations, spectral states and possible connection with jet ejections during the out burst phase. Further,we attempt to connect the observed X-ray variabilities (i.e., ‘class’/‘structured’ variabilities, similar to GRS 1915$+$105) with spectral states of black hole sources. Towards these studies, we consider three black hole sources that have undergone single (XTE J1859$+$226), a few (IGR J17091$-$3624) and many (GX 339-4) outbursts since the start of $RXTE$ era. Finally, we model the broadband energy spectra (3–150 keV) of different spectral states using $RXTE$ and $NuSTAR$ observations. Results are discussed in the context oftwo-component advective flow model, while constraining the mass of the three black hole sources.

We study the properties of sub-Keplerian accretion disk around a stationary black hole, considering bremsstrahlung, synchrotron and Comptonization of synchrotron photons as radiative cooling mechanisms active in the disk. We obtain the solutions of two-temperature global accretion flow (TTAF) and compare it with the results obtained from single-temperature (STAF) model.We observe that flow properties, in particular, the radial profile of electron and ion temperatures differ noticeably in the adopted models for flows with identical boundary conditions fixed at the outer edge of the disk. Since the electron temperature is one of the key factors to regulate the radiative processes, we argue that physically motivated description of electron temperature needsto be considered in studying the astrophysical phenomena around black holes.

We study the radiation properties of an accretion disc around a rotating black hole. We solve the hydrodynamic equations and calculate the transonic solutions of accretion disc in the presence of shocks. Then we use these solutions to generate the radiation spectrum in the presence of radiative heating and coolingprocesses.We present the effect of spin parameter of the black hole on the emitted radiation spectrum. In addition,attention has also been paid to the variation in energy spectral index with Kerr parameter and accretion rate. We find that spectral index becomes harder as the spin parameter changes from negative (accretion disc is counter-rotating with respect to the black hole spin) to a positive value. Finally, we compute and compare the spectral characteristics due to a free-fall flow and a transonic flow. We notice significant differences in highenergy contributions from these two solutions.

Journal of Astrophysics and Astronomy | News

Continuous Article Publication

Posted on January 27, 2016

Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.